1. Field of the Invention
The present invention relates to an input scanner, and more particularly, to the processing of signals in such a scanner.
2. State of the Prior Art
It is known in the prior art to use a linear CCD imager to scan films, such as a radiographic film, to produce a digital record. The film is illuminated at a scanning station by a line source, and it is projected with large demagnification onto the much smaller imager. The film is scanned line by line as it is moved slowly past the scanning station. Because of the clinical significance of unusual details in a radiographic film, there can be very little tolerance for artifacts. Thus, ways have been sought to eliminate the artifacts and increase the resolution in the image. One approach has been to use multiple imagers to provide higher pixel data rates than a single imager can handle.
The signal-to-noise ratio of the data generated by the imagers depends primarily on the level of noise in the analog signal from the CCD imager. Several types of digital signal averaging have been used to reduce the noise level in imaging systems and to improve the dynamic range. One of the most common techniques involves capturing a line of the image several times and adding together the digital results for corresponding pixels. This is a simple and convenient way to improve dynamic range, but the gains are proportional to the square root of the number of samples, and the taking of a number of samples slows the process considerably. A less commonly used method is to sum the digital values of pixels in the line itself; however, this is a relatively expensive way to obtain a better image.